1) Field of the Invention
This invention relates to a method and apparatus for continuous detection and localization of yarn defects in a yarn sheet which is traveling in a plane and which is scanned by light beams for yarn defects such as protruding filaments, broken filaments, fuzzballs, stripbacks, ringers and the like, each light beam interruption triggered by such a yarn defect, thereby triggering a detector pulse.
2) Prior Art
The monitoring of traveling yarns for diameter fluctuations and particularly for protruding filaments, yarn defects, i.e. broken filaments, fuzzballs, ringers, stripbacks and the like, in the production of yarns in the manufactured fiber or textile industry using optical detector devices such as for example light barriers is known.
Such a device for monitoring a single traveling thread or yarn for diameter fluctuations and protruding filaments using a light barrier operating in the infrared region is described in DE 29 33 297 A.
Similar light barriers are used to monitor sheets of some hundred unwinding yarns in the production of warp beams. With this procedure, only relatively coarse yarn defects and broken yarn are identified as defects; these light barriers are unable to recognize broken individual filaments in individual yarns. Localization of the yarn defect at right angles to the yarn direction is generally only possible at huge cost and inconvenience, if at all.
EP 0 296 469 B1 discloses a process for determining quality characteristics of traveling yarns by using defect counters to determine the number of yarn irregularities. The yarn passes through at least three successive defect sensors of the same type whose counting pulses emitted on passage of a yarn section of the freely chosen length L are converted into a length-based average R by disregarding from the averaging any greatly deviant individual measurements as spurious values. The apparatus used to carry out the process consists of at least three defect sensors disposed consecutively in the yarn path, means for measuring the traversing yarn length L and an arithmetic processing unit which sums the counting pulses separately for each sensor to form pulse totals and stores these pulse total values. The totals obtained are tested for spurious values according to predetermined criteria and such values are eliminated. Useful means for measuring the yarn length include any arrangement known for this purpose, for example a measuring roller of a certain circumference which is rotated without slippage by the traveling yarn and whose number of revolutions is recorded. To monitor a sheet of yarn, every individual yarn has to be inspected by such apparatus; the cost is accordingly enormous.
DE 195 26 646 A1 discloses a process for monitoring a traveling yarn sheet by passing the yarn sheet over guide bars upstream and downstream of the monitoring site and sending at least one light beam at right angles to the traveling direction of the yarn sheet and parallel to the yarn sheet plane to photoreceptors. The signals from the photoreceptors are evaluated by an electronic evaluating unit and recorded. At least four photoreceptors are used, of which at least two are disposed successively in the yarn traveling direction and at least two above each other in such a way that there is at least one photoreceptor below and at least one photoreceptor above the yarn sheet plane. All the photoreceptors are disposed in such a way that they form superposed pairs and all the pairs are disposed one behind the other. This known apparatus preferably employs 4 quadrant photoreceptors or multisegmental photocells. The monitoring arrangement is formed by a light source, which can be a laser light source, a lens for parallelizing the light beam, a diaphragm for determining the light beam cross section, a further diaphragm for intercepting stray rays, a lens for focusing light beams and a 4 quadrant photoreceptor or a multisegmental photocell. The technical complexity of this apparatus is enormous. A specific method for localizing a yarn defect at right angles to the yarn direction is not described.
DE 38 32 984 C2 discloses a process and apparatus for indicating broken ends in a yarn sheet traveling in a plane by scanning the yarn sheet with a laser beam at right angles to the traveling direction of the yarn sheet in continually repeated passes and counting the light pulses reflected by the individual ends per passage by means of detectors. The number of light pulses is compared with a target value for the number of individual ends and deviations from the target value are indicated. For this, a multiplicity of detectors are disposed side by side substantially equal distances apart in a row which is perpendicular to the yarn traveling direction and in a plane which is parallel to the yarn sheet plane, in such a way that reception areas overlap. The detectors are oriented in an identical angle, the backbeam angle, to the line of incidence of a laser beam reflected by a rotating mirror, with the yarn sheet. The laser beam is disposed relative to the yarn sheet and relative to the row of detectors in such a way that the angle of incidence of the laser beam reflected by the rotating mirror on the yarn sheet and the backbeam angle are substantially the same. At least three and preferably at least five passes are grouped together in a cycle and the light pulses are counted per pass and compared with the predetermined target value for the number of individual ends. Absent agreement between the two values, a defect signal is generated and counted in a counter. At the end of each cycle, the final value of the counter is compared with a predetermined limiting value and when the limiting value is reached or exceeded the yarn sheet is stopped. Again, the technical complexity of this process and apparatus is comparatively large.
WO93/06466 describes a process for detecting and counting yarn defects in a yarn segment using a camera, a computer and an image processing program. The yarn is recorded by the camera with an intensity which depends on the thickness of the yarn. The recorded image is digitized in the computer by the image processing program and low-contrast points are filtered out. The points which remain are grouped together into continuous areas whose size is categorized into predetermined size classes and stored. The process makes it possible to count yarn defects, for example. yarn impurities, objectively and reproducibly. This process is not intended for inspecting a fast-traveling yarn sheet for defects in individual ends.
WO93/19359 discloses a process and apparatus for detecting impurities in a textile test material. For this, the test material is illuminated for at least two locations and the light reflected by the test material is measured by receptors and in addition to the reflection the diameter or diameter changes of the test material are measured. The measured signals obtained are combined and the resulting signal is examined for deviations from a predetermined value. If a deviation is ascertained, an impurity is present in the test material. The checking of a fast-traveling yarn sheet for yarn defects is not possible by this process and the apparatus intended for it.
It is also known for a yarn sheet to be monitored using commercially available single light barriers and to be stopped in the event of a yarn defect occurring. In this process, the operating personnel subsequently has to search for the yarn defect and to cut it out, for example, and subsequently to piece the yarn back together by means of a knot. The only information to guide the search for the yarn defect that the operating personnel has available is that the position of the yarn defect is localized in the yarn traveling direction. This position follows from the original traveling speed of the yarn sheet and the speed deceleration to stopping by the brakes which stop the yarn sheet. There is no information about the position of the yarn defect at right angles to the traveling direction of the yarn sheet, so that the operating personnel has to scour the entire width of the yarn sheet, which can be up to about 300 cm, to find the yarn defect.
It is an object of the present invention to design a process and apparatus at minimal cost and inconvenience in such a way that the position of a yarn defect in a traveling yarn sheet at right angles to the traveling direction is quicker to find than in existing processes and apparatus.
This object is achieved according to the invention by the yarn sheet passing through a measuring arrangement which comprises light barriers which are made up of light sources and detectors being arranged relative to each other in a V-shape and also evaluating means, the light beams of the light barriers extending parallel to the yarn sheet plane, at constant speed and the travel distances of the individual ends from one light barrier to the next differing in length.
Since all ends of the yarn sheet have the same velocity, the difference in travel length gives rise to a time difference between the light barriers responding. This time difference is a measure of the position of the yarn defect at right angles to the traveling direction of the yarn sheet. The position of the yarn defect in the traveling direction of the yarn sheet (stop position) is, as described above, defined by the fact that at least one of the light barrier signals is also used to stop the yarn sheet.
In carrying out the invention, the light beams of two adjacent light barriers which are disposed in a V-shape either converge or diverge relative to each other from the light sources.
In further development of the invention, the time difference T1,2 between the trip times of a yarn defect through the two light barriers in a V-shaped arrangement of two light barriers in which the light beam of one light barrier is perpendicular to the traveling direction of the yarn sheet is determined by the equation T1,2=S*tan(xcex1)/v where S is the distance which is perpendicular to the traveling direction of the yarn sheet between the point of intersection of the light beams of the two light barriers and the yarn defect, xcex1 is the angle between the light beams of the light barriers and v is the velocity of the yarn sheet.
The angle xcex1 is in the range from 5xc2x0 to 85xc2x0 and especially in the range from 10 to 45xc2x0.
In general development of the process, the time difference T1,2 between the trip times of a yarn defect through the two light barriers in a V-shaped arrangement of two adjacent light barriers which are both inclined relative to the normal to the traveling direction of the yarn sheet, the first triggered light barrier including an angle xcex2 with the normal that is positive in the counter clockwise direction and negative in the clockwise direction with regard to the point of intersection of the light beams of the two light barriers is determined as per the equation
T1,2k*S*tan xcex1/vxe2x80x83xe2x80x83(1) 
where the correction factor
k=(1+tan2xcex2)/(1xc2x1tan xcex1*tan xcex2)xe2x80x83xe2x80x83(2) 
S is the distance perpendicular to the traveling direction of the yarn sheet between the point of intersection of the light beams of the two light barriers and the yarn defect, xcex1 is the angle between the light beams of the light barriers and v is the velocity of the yarn sheet. The (+) sign in the denominator of equation (2) holds for a divergent course of the light beams, and the (xe2x88x92) sign for a convergent course.
In apparatus for the continuous detection and localization of yarn defects in a yarn sheet traveling in a plane, comprising light barriers for detecting detector pulses triggered by fuzzballs, broken filaments, protruding filaments, stripbacks, ringers and the like yarn defects, at least two light barriers whose light beams form an angle xcex1 with each other are disposed at right angles to the traveling direction and immediately above or below the yarn sheet and parallel to the yarn sheet plane and each or every light barrier comprises a light source and a detector plus associated evaluating means.
In execution of the apparatus, the angle xcex1 between the light beams of two light barriers is in the range from 5xc2x0 to 85xc2x0 and especially in the range from 10 to 45xc2x0.
In further development of the apparatus, the detectors are connected via amplifiers and signal-shaping circuits to evaluating means which determines the time difference Ti,i+1, where i=1,2,3, . . . nxe2x88x921 from the trip times of a yarn defect from one light barrier to the next light barrier, where n is the number of light barriers.
In a further embodiment of the apparatus, there are three light barriers whose light beams have a common point of intersection and form an angle xcex1 between the first and the second light barrier and also an angle xcex1xe2x80x2 between the second and third light barrier that have the same magnitude.
In a similarly possible embodiment, there are four light barriers, the light beams of the first and second light barriers forming an acute angle xcex1, and those of the third and fourth light barriers forming an acute angle xcex1xe2x80x2. In this embodiment, the angles xcex1 and xcex1xe2x80x2 advantageously have the same magnitude, but they can also have different magnitudes. The angles xcex1 and xcex1xe2x80x2 are each in the range from 5 to 85xc2x0 and especially in the range from 10xc2x0 to 45xc2x0. The angles are chosen so that each individual light barrier captures or monitors the entire yarn sheet.
In execution of the invention, each or every light barrier comprises a light source and an associated detector and the detectors are connected via amplifiers and signal-shaping circuits to evaluating means in which the time differences Ti,j where i,j=1,2, . . . nxe2x88x921, ixe2x89xa0j are determinable from the travel times of a yarn defect from one light barrier to each or every one of the other light barriers, where n is the number of light barriers. Preferably, the light sources are laser diodes. If desired, a plurality of light sources may be replaced by a single light source. This single light source generates a corresponding number of light beams in a known manner by prismatic beam splitting.
In further execution, the time difference Ti,i+1, between the trip times of a yarn defect through two adjacent light barriers i and i+1 is predetermined by the yarn velocity v and the geometry of the light barrier arrangement as a function of the distance Si,i+1 of the point of intersection of the light beams of these two light barriers to the yarn defect normal to the yarn traveling direction and the angle xcex1i,i+1 between the light beams as per the equation Ti,i+1=k1*Si,i+1* tan xcex1i,i+1/v where i=1, 2, 3, where xcex112, xcex123 and xcex134 are the angles between a first and second light barrier, between a second and third light barrier and between a third and fourth light barrier and ki is a correction factor which corrects for the inclination of the i-th light barrier in relation to the normal to the traveling direction of the yarn sheet.
The correction factor ki=(1+tan xcex2i2)/(1xc2x1tan xcex1i,i+1*tan xcex2i) where i=1, 2, 3 includes the angle xcex2i which reflects the inclination of the i-th light barrier in relation to the normal to the traveling direction of the yarn sheet and the (+) sign in the denominator indicates that the adjacent light barriers diverge and the (xe2x88x92) sign indicates that they converge.
When all light beams have a common point of intersection or lie on a straight line which is parallel to the yarn sheet, Si,i+1=S will have the same magnitude for all light barrier pairs.
Owing to the limited time resolution of the measuring system, the distances Si,i+1 or S can only be determined with a certain locational deviation LA as will be more particularly described in what follows.